Over the last forty years, an effort has been underway to eliminate the mechanical joints in railroad tracks. That effort has largely involved constructing tracks having continuous rails by welding or otherwise joining together the ends of the adjacently spaced rail sections, forming a structure sometimes referred to as continuous welded rail track. The technology associated with the construction of CWR track is well known in the prior art.
Because all of the rail sections of continuous rail track are connected, continuous rail track can be particularly sensitive to fluctuations in the ambient temperature of the track and surrounding environment, such as seasonal variations in the ambient temperature resulting in variations in the rail temperature. In tropical climates, the ranges between the temperature extremes are generally moderate, which does not pose a substantial problem for rail systems. In temperate climates, however, such as those in the United States, Asia, Australia and Europe, the ranges of temperature extremes are sufficient to cause catastrophic, temperature induced failures in rail systems, including both rail pull-apart and track-buckle failures, as hereinafter described.
For example, an unanchored 100-mile length of continuous rail in certain areas of a temperate climate could experience a change in length of over 600 feet from one seasonal temperature extreme to the other. By anchoring the rail to railroad ties, changes in the overall length of the rail can be largely prevented but, instead, resultant localized longitudinal stresses are created internally in the rail.
As the rail segments of CWR track are initially installed and anchored to a road bed, each of the rails has zero longitudinal stress. The temperature at which the continuous rail track is installed is sometimes referred to as the rail neutral temperature (“RNT”).
As the ambient rail temperature falls below the RNT, tensile longitudinal stresses are created internally in each rail segment of the continuous rail track due to the greater thermal coefficient of expansion of the metal rails relative to that of the underlying road bed. If the difference between the reduced ambient rail temperature and the RNT is extreme, the tensile stresses in the rails can potentially attain sufficient magnitude to actually cause rail segments in one or both continuous rails to pull apart. Fortunately, pull-apart failure can easily be detected by establishing an electrical track circuit using the rails as part of the conduction path, which becomes “open” if one of the rails of the continuous rail track pulls apart.
Likewise, as the ambient rail temperature climbs above the RNT, compressive stresses are created internally in each of the rails of the continuous rail track. If the difference between the elevated ambient rail temperature and the RNT is extreme, the compressive stresses in the rails can potentially attain sufficient magnitude to actually cause the track panel to buckle. The compressive stress required to cause any particular rail to buckle depends on a number of factors, including the absolute temperature, the difference between the ambient rail temperature and the RNT, and the condition of the ballast, for example.
Such buckling, previously considered random and unpredictable, is a major source of derailments. The ability of a train to negotiate a lateral track panel displacement, which is typical of track-buckle, is minimal. As a result, track-buckle poses a substantially greater risk of derailment than does a rail pull-apart since the former cannot be detected by a conventional track circuit.
Although various methods, systems and apparatus have been developed to measure and/or determine longitudinal stresses in a rail of a continuous rail track, none of them have been used to accurately determine whether a section of continuous rail track is within specific safety limits. Consequently, there is a need for systems and methods that address the shortcomings of prior art rail stress identification and provide a more accurate determination of rail performance within prescribed safety ranges.